The objectives of this randomized, double-blind positive-controlled, parallel study is to evaluate whether a selective serotonin antagonist has clinical activity as an antipsychotic agent and is devoid of extrapyramidal adverse effects and of hyperprolactinemi. Another objective is to evaluate the antipsychotic activity of MDL in schizophrenic patients who have been without antipsychotic treatment for at least 2 weeks. Secondary objectives are to demonstrate the safety, tolerability, and pharmokinetics.